This application claims the priority of German application 196 15 542.8-52 filed in Germany on Apr. 19, 1996, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device for determining the engine load for an internal combustion engine.
Such devices are used to determine the air mass passing into a respective cylinder of the engine, per working cycle (i.e. the load), at every engine operating point as accurately as possible, so that precisely the correct associated quantity of fuel can be injected, thus permitting an optimum mixing ratio between the air and fuel, and achieving optimum combustion. Since the air mass flowing into the respective cylinders cannot be measured directly, the engine load must be determined indirectly by means of physical variables associated therewith. These include the intake manifold pressure, the throttle-valve air mass flow rate measured upstream of the throttle valve, and the throttle valve angle, in each case in conjunction with the instantaneous engine speed. In this context, usually a so-called hot-film air mass flow rate meter arranged at the throttle valve is used as a mass air flow rate sensor.
While the determination of the engine load is less problematic during steady-state operation of an engine, during non-steady-state operation the dynamic behavior of the engine components involved (in particular of the intake manifold and of the engine sensor system) present additional difficulties for this determination. Thus, for example, the measurement of both the throttle-valve air mass flow rate and of the intake manifold pressure is disturbed by harmonically vibrating components, caused, inter alia, by the piston travel movement in the individual cylinders, flow influences in the valve openings and the acoustic properties of the intake manifold.
The conventional method for acquiring a non-pulsating engine load value is to form mean values over a number of measurements, depending on the frequency of the pulsation to be suppressed. For example, the throttle-valve air mass flow rate, accompanied by evaluation of the inlet valve opening time and corrected by an engine-speed-dependent characteristic diagram, is measured to determine the air mass passing into the engine. Alternatively, either the throttle valve angle is used in conjunction with a throttle valve angle/engine speed characteristic diagram, or the intake manifold pressure is used in conjunction with the instantaneous engine speed, to determine the load. Such characteristic-diagram-assisted load-determination methods generally require a high application expenditure in the engine control units. While the formation of mean values can achieve satisfactory results in the steady-state case, in the non-steady-state case it provides delayed, and thus correspondingly erroneous, values owing to the low pass filter behavior. When the throttle-valve air mass flow rate measurement is used to determine the engine load, a further source of errors occurs when there is a sudden change in the throttle valve position. This is because such a sudden opening or closing of the throttle valve causes a rapid increase or decrease of the air mass flow rate, which results in a change in the intake manifold pressure, but is only partly expressed in a corresponding change in the air mass flowing into the cylinders.
It is generally known in open-loop and closed-loop control technology to use a so-called Kalman filter to acquire estimated values for state variables which are of interest. A Kalman filter models the real process by means of a prescribed filter algorithm, for which so-called input values (usually control values of the process) are fed to the filter on the input side as fixed values, and so-called measured variables (usually values sensed in the process) are fed to it as variable values. The modelling can take place linearly or non-linearly with the aid of a so-called expanded Kalman filter. The properties of Kalman filters are well know to those skilled in the art.
German patent document DE-OS 41 22 391 A1, discloses the use of a Kalman filter to determine engine speed by means of a position angle measured by a position sensor, so that a mechanical engine speed sensor can be dispensed with German Patent Document DE-OS 34 16 812 A1 discloses an arrangement which uses a Kalman filter to regulate process variables in motor vehicles, such as the driving speed or idling speed.
German patent document DE-OS 43 41 132 A1 discloses an air/fuel ratio estimation device for multi-cylinder internal combustion engines, in which an arithmetic unit of a regulator estimates the air/fuel ratio according to model equations of a Kalman filtering operation. The primary measured variable used in these model equations is the output signal of an air/fuel ratio sensor whose sensing element is arranged in the common exhaust-system section of all the cylinders and whose sensor signal thus represents an air/fuel ratio which is determined indirectly by means of the oxygen concentration of the exhaust gas and represents a mean value over all the cylinders. Further sensor signals fed to the regulator unit are those of a throttle valve position sensor, an intake manifold pressure sensor and of a crank angle sensor.
German patent document DE-OS 41 00 006 A1 discloses the use of a Kalman filter in a mass flow rate measuring unit with a measurement tube functioning as a Coriolis transducer. The measurement signal of the latter is processed with the aid of the Kalman filter in order to estimate flow rate.
A device disclosed in German patent document DE 39 34 498 A1 is intended for regulating the fuel supply for an internal combustion engine. The quantity of air actually taken into the cylinders, in particular during operating phases with rapid acceleration, is estimated in that a regulator unit generates an intake-air-quantity correction signal according to the change in the output signal of a throttle valve position sensor and corrects the output signal of an air quantity sensor by the correction intake-air value.
A control unit for motor vehicles disclosed in German patent document DE-OS DE 44 22 184 A1 has an arithmetic unit for calculating the air mass flowing into a cylinder of an internal combustion engine, in accordance with analytical relationships in which the intake manifold pressure and/or the throttle-valve air mass flow rate constitute calculated, and additionally measured, operating parameters. The algorithm is structured in such a way that it corrects itself as a function of the difference between the calculated operating parameter value and the measured operating parameter value.
One object of the present invention is to provide an engine-load-determination device of the type described above, which reliably determines the engine load, with comparatively little expenditure, even during non-steady-state operation.
To achieve this object the engine-load-determination device according to the invention uses a Kalman filter, to which at least the engine speed is provided as an input variable. One or more of the three variables intake manifold pressure, throttle-valve air mass flow rate and throttle valve angle are also input as variables measured by the respective sensors. From these inputs, the Kalman filter estimates values for the intake manifold pressure and throttle-valve air mass flow rate, based on a suitable model equation and on the known Kalman filter algorithm. The last-mentioned variable is expediently acquired indirectly from estimated values for the effective throttle-valve flow cross-section.
It is apparent that, with such a Kalman filter, highly reliable engine load values can be determined, even during nonsteady-state operation, and even in the case of the failure of one or two of the three sensors for measuring the intake manifold pressure, the throttle-valve air mass flow rate and the throttle valve angle. In conventional systems, the failure of the throttle valve angle sensor, for example, would cause the engine control to fail; the device according to the invention, however, is makes it possible, even in this case, to carry out a reliable dynamic determination of the engine load on the basis of a still intact intake manifold pressure sensor or throttle-valve air mass flow rate sensor.
In one embodiment of the invention, the state variables used for the Kalman filter are the intake manifold pressure, the effective throttle-valve flow cross-section, its first derivative and the air mass flow rate via the throttle valve. The measured variables fed to the Kalman filter are the intake manifold pressure, the throttle valve angle and the throttle-valve air mass flow rate acquired by the hot-film air mass flow rate meter. The effective throttle-valve flow cross-section is treated in the model equations of the filter algorithm as a time-correlated noise variable. With this implementation of the Kalman filter, highly precise and reliable engine load values can be acquired, even in the case of rapid load changes during non-steady-state operation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.